Project Summary Adolescent and young adult men who have sex with men (YMSM) are the only group in the U.S. in which rates of new HIV infections are increasing, which reflects a large disparity relative to heterosexuals. Steady or main partner relationships account for a substantial proportion of new HIV infections in YMSM. Among YMSM a serious relationship status is perhaps the strongest predictor of condomless anal intercourse (CAI), and pre- exposure prophylaxis (PrEP) may be discontinued in a relationship. Romantic relationships also provide myriad benefits, including promotion of mental, behavioral, and physical health. Despite the critical importance of romantic relationship factors for HIV prevention, the vast majority of studies and interventions focus on individuals. We conducted formative research on coupled YMSM through an NIH R21 from which we developed an innovative couples-based intervention that addresses the continuum of HIV prevention and care for YMSM couples. The 2GETHER program integrates couples- and group-based modalities and is innovative in its design to address HIV transmission risk in couples regardless of serostatus; couples learn to utilize behavioral and biomedical approaches to prevent both HIV acquisition and transmission, with an overarching emphasis on improving relationship functioning. 2GETHER further encourages uptake of couples-based HIV testing for HIV-/unknown YMSM and medication adherence and engagement in care for HIV+ YMSM. We established feasibility, acceptability and preliminary efficacy of 2GETHER in a pilot trial of coupled YMSM (N=60 couples; 120 individuals), including significant decreases in HIV transmission risk behavior. Based on our highly successful pilot, we propose to test the efficacy of 2GETHER in large-scale randomized controlled trial (RCT). We will: (a) enroll racially diverse coupled YMSM; (b) randomize couples to either the 2GETHER intervention or attention-matched positive affect skills program for couples; (c) measure intervention outcomes through 12 months post-intervention. Analysis of study outcomes will utilize both individual- and dyadic-level data. Primary HIV risk behavioral outcome: an individual-level dichotomous variable indicating presence of CAI with a serodiscordant or unknown status partner. Exploratory analysis will calculate an innovative variable that accounts for the relative risk of sexual behaviors with partners of different serostatus, accounting for biomedical prevention. Primary biomedical outcome: Chlamydia/Gonnorhea incidence in individuals. Secondary dyadic-level HIV risk outcomes: concordance/discordance in relationship sexual agreement type and presence of agreement breaks. Secondary individual-level engagement in care outcomes: HIV testing uptake (HIV- men) and medication adherence (HIV+ men). In the context of increasing fatigue for HIV prevention, a healthy relationships program for coupled YMSM presents an opportunity to reinvigorate HIV prevention. Further, in the era of treatment as prevention, we must develop transmission prevention strategies for MSM regardless of serostatus that address the full continuum of prevention and care.